The hydroesterification or hydrocarbomethoxylation of olefins and alcohols catalyzed by cobalt catalysts is known, being described for example in U.S. Pat. No. 2,542,767. The use of a small amount of pyridine in combination with hydrogen is known to improve the selectivity of the hydroesterification of propylene. This is described by A. Matsuda and H. Uchida in Chem. Soc. Japan Bull. 38, 710-715 (1965). Relatively large amounts of pyridine alone are also known to promote propylene hydroesterification as disclosed by V. Gankin et al, in Zh. Prikl. Khim. 40, 1862-1864 (1967).
Other discussions of the reaction of olefinic materials with CO in the presence of a cobalt catalyst and a pyridine are contained in U.S. Pat. No. 3,507,891, in U.S.S.R. Pat. No. 173,754 (Sept. 25, 1965), and in Japanese Pat. No. 12,854 (July 21, 1966); in Chem. Abstracts, Vol. 68, 12411b (1968) (page 1169); by Ghankin et al, Zh. Prikl. Khim. (Leningrad) 14 (11) 2582-5, Nov. 1968; and by G. Natta, Brennstoff-Chem., 36, 176 (1955 ).
One of the problems encountered in prior art processing is emphasized by U.S. Pat. No. 3,507,891 which uses certain substituted pyridines rather than pyridine because of the problem that with pyridine a direct distillation of product containing the complex formed 10 percent or more metallic cobalt which could not be reconverted readily to catalyst. The present invention avoids this problem and provides a way to recover and recycle the catalyst when using various pyridines, even pyridine itself. As a result, one can obtain high conversion characteristic of the use of pyridine-containing systems without having to use substituted pyridines to overcome the catalyst recycle problem. Athough the present invention is suitable for use with pyridine itself, it also may be applied in conjunction with the substituted pyridines which are useful catalysts such as those set forth in U.S. Pat. No. 3,507,891.
A preferred prior art process for the recovery and recycle of a large part of the cobalt values is disclosed in U.S. Pat. No. 3,856,832 wherein the hydroesterification reaction mixture containing ester product, alkanol and cobalt catalyst obtained on reacting olefin, CO and alkanol is contacted with a normally liquid hydrocarbon in an amount sufficient to dissolve the ester product and then the normally liquid hydrocarbon phase is separated from the alkanol phase. Most of the cobalt catalyst goes to the alkanol phase in active form and is suitably recycled to the hydroesterification reaction. In some instances further improvement in cobalt recovery is desired and it is to this end that the present process is directed.